1. Field of the Invention
This invention relates to equivalent circuit models for substrate mounted components, and more particularly to the generation of a global equivalent circuit model for substrate mounted circuit components applicable in a CAD or CAE system wherein the model is based upon certain substrate dependent characteristics and scales according to the nominal component characteristics.
2. Background of the Invention
In the world of electronic circuit component design and fabrication, particularly in the field of RF and microwave circuit design, there is a great deal of reliance upon the availability of reliable, accurate component models. Where resistors, transistors, inductors, capacitors and other components are mounted directly upon a printed circuit board, or “substrate”, it is often necessary to prepare an electrical circuit model that provides an accurate representation of a component's response and behavior. Often, models of this nature are used in conjunction with computer-aided-engineering (CAE) or electronic design automation (EDA) software. Methods currently in use to predict the response of these components include the use of scattering parameter measurements, mathematical functions and circuit parameter extraction-based models.
Measurement-based models can provide an accurate representation of a component's response, yet have been limited because de-embedding the component fixtures or its surroundings is not taken into consideration. In addition, measurement-based models require a large amount of computer storage allocation. The effects of variations in the height, the width and the dielectric constant of the substrate upon which the component rests are largely ignored.
The majority of equation-based models fail to take into consideration printed circuit board, parasitic or frequency-related effects. Further, the inherent complexity in deriving these formulas usually compromises their accuracy and range of application.
The use of equivalent circuit models, on the other hand, generally provides physical insight of the component and its fixture, requires minimal storage and memory allocation, and offers fast simulation time. However, most if not all equivalent circuit models are lacking in two very critical areas. First, as mentioned above, these models largely ignore the PCB environment. While some models may attempt to represent substrate characteristics, for example, representing bond-pad interaction in a ceramic multilayered capacitor model by a microstrip gap capacitor, the effect is insignificant, as other parasitic effects are ignored. Models that do not account for substrate effects are likely inaccurate. Second, and equally as critical, is the inability of present models to provide a general or “global” model that scales directly with component size. As an example of this second area, if a design engineer does not know the exact component value to use in a particular part of an electrical schematic, it may be necessary for the design engineer to manually choose individual models until the correct component value is found.
Therefore, in addition to creating an accurate substrate-dependent model for electrical circuit components, there is also a need in the art, particularly to facilitate CAD optimization, to create a global model that may be used to represent each family of components, i.e. one model that covers the entire range of values, for example, from 1 picofarad capacitors up to 1800 picofarad capacitors, to facilitate circuit optimization.
Accordingly, what is needed in the art is a substrate-dependent equivalent circuit model wherein the equivalent-circuit parameters utilized in the model are made to vary with changes in the substrate, as well as a global equivalent-circuit model that provides one “general” model that can be applied to a large family of components of varying size. Further, a more accurate and versatile method for analyzing surface mount performance of various types of circuit components is needed in order to significantly reduce bench time as well as the number of design cycles necessary to design new electronic products.
It is, therefore, to the effective resolution of the aforementioned problems and shortcomings of the prior art that the present invention is directed.
However, in view of the prior art at the time the present invention was made, it was not obvious to those of ordinary skill in the pertinent art how the identified needs could be fulfilled.